I noticed three issues with the mobile PIE device preview json profiles:
The easiest repro is to view the json files in comment
In-editor repro is
1. Enable mobile PIE with preview device in Editor Preferences
2. Load SunTemple
3. Use PIE > Mobile Preview > Android > Nexus 5
RESULT: The preview uses lower spec quality settings (no metal, no specular)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-46995 in the post.